Variable focal length objective having eight axially spaced lenses



Oct. 24, 1967 c. BAUR ETAL 3,348,898

VARIABLE-FOCAL LENGTH OBJECTIVE HAVING EIGHT AXIAL-LY snow wussg Filed Nov. 1963 INVENTOR.

CARL BAUR CHRISTIAN ()TZEN 7 0M fifller- United States Patent 3 Claims. 01350-184 The present invention relates to an adjustable projection objective, and more particularly to a wide aperture projection objective of constant length whose focal length can be varied.

Adjustable projection objectives are known in which a negative bi-concave singlet is adjustable in the direction of the optical axis of the objective for varying the focal length of the objective. This type of objective is particularly used for 8 mm. motion picture film. The range of focal lengths achieved by known objectives of this type is between mm. and 25 mm., however, the maximum aperture is f:l.6 or f:l.5. A disadvantage of the known adjustable objectives is the substantial chromatic magnifi-v cation aberration, particularly in the wide angle position when the focal length is adjusted to be a minimum.

It is one object of the present invention to provide an adjustable projection objective which overcomes these disadvantages of prior art objectives, and has a wider maximum aperture for the same range of adjustment of the focal length.

Another object of the invention is to provide an adjustable projection objective having a wider aperture than known objectives of this type, but having nevertheless small dimensions, particularly in the front part of the objective.

Another object of the invention is to provide an adjustable projection objective which has no distortion in the middle region of the adjusted focal length range, and has in the end regions of the range of adjustment, negligible barrel distortion and cushion distortion.

Another object of the invention is to reduce chromatic magnification aberration to approximately one-quarter of the residual chromatic aberration of known projection objectives whose focal length can be adjusted.

Another object of the invention is to provide an adjustable projection objective whose maximum aperture is approximately one stop greater than the maximum aperture of similar known projection objectives, while spherical aberration, coma, astigmatism, chromatic aberration,

rected adjustable projection objective which can be ecO- nomically manufactured and is composed of lenses of simple shape, including lenses having planar surfaces and symmetrical lenses.

With these objects in view, the present invention relates to an adjustable projection objective whose focal length can be varied. One embodiment of the invention comprises eight axially spaced lenses, the first, fourth, fifth, sixth and eighth lenses in the order from the front to the rear being positive, and the second, third and seventh lenses being negative.

In accordance with the invention, the second and third lenses, which are separated by a constant axial air space, are together forwardly and rearwardly movable in the direction of the optical axis of the objective to vary the focal length of the objective.

In accordance with the preferred embodiment of the invention, the absolute sum of the powers of refraction of the front and rear surfaces of the second lens is greater than the absolute 'sum of the powers of refraction of thefront and rear surfaces of the third lens, but smaller than Patented Oct. 24, 1967 twice the last mentioned absolute sum. In this manner, spherical aberration, coma, and astigmation are highly corrected.

Preferably, the first and fourth lenses are constructed in such a manner that the absolute sum of the powers of refraction of the front and the rear surfaces of the fourth lens is between two times and three and one-half times the absolute sum of the powers of refraction of the front and rear surfaces of the first lens in the order from the front to the rear of the objective. This results in a very favorable correction of the distortion so that-the same is practically zero in the middle of the range of the adjustment of the focal length, while near the ends of the range of adjustment, negligible barrel distortion and cushion distortion takes place.

Chromatic coma is substantially improved as compared with prior art objectives, although the maximum aperture is greater by one stop than the aperture of known objectives. This is accomplished by using for the second and third negative and adjustable lenses, glass having Abbe numbers greater than 55, and by using for the first and fourth positive lenses, glass having Abbe numbers greater than 56. This selection of glass reduces the chromatic magnification aberration to one-quarter as compared with the residual chromatic aberration of known projection objective having variable focal lengths.

The objective according to the present invention can be very economically manufactured since it remains fully corrected when the first and fifth lenses are piano-convex, the third and seventh lenses are plane-concave, the second lens is symmetrically bi-concave with radii of curvature on both refraction surfaces, and the fourth and eighth lenses are symmetrically bi-convex with equal radii of curvature on opposite refraction surfaces. As a result, an objective according to the present invention which has sixteen refraction surfaces, has four planar refraction surfaces, and three lenses in which both surfaces have the same radii of curvature.

In addition to the economical manufacture of the lenses, the assembly is facilitated, and it is easy to assemble the objective, since a reversing of the symmetrical lenses is immaterial, and a reversal of the lenses having planar surfaces is immediately noticeable.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is an axial sectional view of an adjustable projection objective according to one embodiment of the invention, and illustrating a first adjusted position of the objective;

FIG. 2 is an axial sectional view corresponding to FIG. 1, but illustrating another adjusted position of the objective; and

FIG. 3 is an axial sectional view corresponding to FIGS. 1 and 2, but illustrating a third adjusted position of the objective.

Referring now to the drawings, the objective includes eight lenses L L L L L L L and L the .subscripts indicating the order of the lenses from the front to the rear so that lens L, is located in front and lens L is located in the rear of the objective.

All lenses, except lenses L and L are fixedly mounted in a barrel, not shown, while lenses L and L are mounted for movement together between the end position shown in FIG. 1, the intermediate position shown in FIG. 2, and the other end position shown in FIG. 3. The means by which the adjustable lenses L and L, are axially shifted are of a conventional nature, and therefore not illustrated.

Lens elements L to L have thicknesses d d d d d d d,, and d respectively. The front surface of the first lens L has a radius of curvature R and the rear surface of this lens has a radius of curvature R which is infinite since the rear surface of lens L is planar. The front surface is convex to the front, so that lens L is a piano-convex lens.

The second lens L is bi-concave and symmetrical so that the radii R and R of the two refraction surfaces are equal. A variable air space 1 separates lenses L and L The third lens L is piano-concave, the concave front surface having a radius of curvature R while the radius R of the planar rear surface is infinite. A constant air space 1 separates the two negative lenses L and L The fourth lens L is bi-convex and symmetrical, having equal radii of curvature R and R A variable air space l separates lenses 1. and L The fifth lens L is lano-convex and positive, the front face of the lens having a radius of curvature R and the rear face having an infinite radius of curvature R An air space l separates lenses L .and L The sixth lens L has a front surface convex to the front with a radius of curvature R and a rear surface convex to the front and having a radius of curvature R An air space 1 separates lenses L and L The seventh lens L is plane-concave. The front face is planar and has an infinite radius of curvature L while the rear surface has a radius of curvature R An air space 1 separates lenses L and L, from each other.

The eighth lens L is bi-convex and symmetrical, the front and the rear surfaces of the lens having equal radii of curvature R and R An air space 1 separates lenses L7 and L8.

The glass of lenses L and L has Abbe numbers greater than 55, and the glass of lenses L and L has Abbe numbers greater than 56.

In accordance with the invention, the absolute sum of the powers of refraction of the front and rear surfaces of the lens L is greater than the absolute sum of the powers of refraction of the front and the rear surfaces of the lens L but smaller than twice the last-mentioned absolute sum which may be mathematically expressed as follows:

(1) An An An An An An R5 R6| 123 Rf 2 R5 Ra so that spherical aberration, coma, and astigmatism are highly corrected.

Preferably, the absolute sum of the powers of refraction of the front and rear surfaces of lens L is between two times and three and one-half times the absolute sum of the powers of refraction of the front and rear surfaces of the lens Li which can be mathematically expressed as follows:

An An An An 2 We wherein f is the focal length of the respective lenses L L L L Unless the objective is constructed accordingly, an aperture of 1:1.1 cannot be QbCQi QQ f 1 q j e having the wide range of focal length adjustment of the present invention with a desirable small diameter of the front elements of the objective.

The following examples of preferred embodiments of the invention are illustrative for projection objectives according to the present invention:

Example I The length of the objective is 2.78209F, and its maximum aperture is f:1.1.

Lenses Radil of Curvature Thicknesses and Airspaces R =+3.10878f L1 dt=0.12500f l1=see table below R3 -3.54321f L1 dg=0.10947f Ii=0.07900f R 2.37372]' L: da=0.10947f R5 co la=see table below R =+2.25261f L4 d4=0.13673f l4=0.00800f R =+1.41669f L5 d5=0.19000f l =0.00500f R =+0.56300j L d=0.16880f R1g=+2.02380f lu=0.04621f R13: on L d1=0.25475f Ri4=+0.33093f l =0.25194f R =+0.82575f La d3=0.13000f Index of Refraction n Dispersive Index 11 n1=1.56873 v1=63.12 m=1.51680 0 :64.20 1t3=1.51680 v3=64.20 m=1.56873 v4=63.12 7L5=L62041 l75=60.29 m=1.6204l v@=60.29 n =1.78470 u1=26.10 m=1.75496 v 53.28

Variable Airspaces Rear Intercept Focal Length Length l =0.08749f la=1.08023f 0 29315) 0.75172] lr=0.68768f la 0.48004f 0 31374] 1.00) l1=1.12772f ls=0.04000f 0 32521) 1.25248f Lenses Powers of Refraction Lenses Powers of Refraction An/R An/R L Front surface +0.18294/f L Front surface +0.43792/f Rear surface 0 Rear surface 0 L Front surface 0.14586/f L Front surface +1.10197/f Rear surface 0.14586/f Rear surface 0.30656/f L Front surface -0.21772/f L Front surface 0 Rear surface 0 Rear surface -2.37120/f L Front surface +0.25248/f L Front surface +0.91427/j Rear surface +0.25248/f Rear surface +0.91427/f In the above table, 11 is the index of refraction for the D line of the spectrum having a wave length of 587.6 m The values for the variable air spaces 1 and are given for the three positions illustrating in the drawings in FIGS. 1, 2 and 3.

Example II The projection objective has a total length of 2.76866F,

and a maximum of f: 1.1.

6 Example III 5 Lenses Radii 0t Curvature Thickness and Alrspaces Lenses Radii of Curvature Thicknesses and R1 =+3.17793f Auspaces L1 d =0.12500f w z t bl b 1 1=see a e e ow +3'15830f a 012500 R3 f Rz =00 f L1 d1=0.07250f li=see table below R4 =+3-84882f l 12791 R; =-3.2os40 R 318W f L; d,=0.07250f L 5 d 07250].

R =+3.26340f l Ram R --2 95840 P012791 la=see table below 5 f R =+2 51876] L: R f d4=013673f a m l -la=see table below 25187Gf l -0 00800f R =+2.67075f R9 =+1 16025]. L4 d4= f L5 d 0 21600 RE =-2.67075f Emma ZFO'OOSW l5=0.00500f R -+1.05955f d 19000 R1i=+0.56300f R :00 f L0 d =0.16480f l =0 00500; Rm=+2.14680f la=0.04621f Ru+0.58450f Rum LB f L7 (17:0 19700! 1z=+ RH=+034065I R 16:0.04621f 2D 17 0 28051}.

13 L1 R 0 3352M d1=0210001 Lam Rlirfo-sfismf dFmmf 3 f z1=0.2s590 RIF-036810! R =+0.85 10 L8 da=0.13000f R1e=0.35310f 3 Lenses Index of Retraction n Dispersive Index 0 n1=1.56873 01:63.12 m= .51680 v1=64.20 m= .510s0 va=64.20 m= v4=gg2 'Il Lenses Index of Refraction n Dispersive Index :1 3: 62041 33 60 28 m=1.56873 v1 .12 4328 n;=l.5l680 v2 .20 40 m=1.5l680 v3 .20 m=1.56s73 v4 .12 1L5=L23041 v .3 =1. -041 v 22:1.78470 v: .10 Variable Airspaces Rear Intercept Focal Length 1t5=1.75496 11g .28 Length l1=0.07800f l =1.l1451f 0.297401 0.74834] l1=0.69769f l3=0.49481f 0.31642; 0.99791! l =1.15251f l =0.0400o/ 0.3265lf 1.24751 Lenses Powers of Refraction Lenses Powers of Refraction Variable Airspaces Rear Intercept Focal Length ATE/R An/R Length L Front surface -|0.17896/f L Front surface +0.53472/f Z =0.07s0c l =1.11611 0.29737] 0.74884f 1 5 Zi=0.69872' l=0.49539f Ogfilgf lgg'se Rear surface 0 Rear surface 0 lFl'lsulf ZFO'OLOOOI f f In Front surface 0.13427/f L Front surface +1.10197/f Rear surface 0.13-t27/f Rear surface -0.28399/f L Front surface 0.22294// L Front surface 0 Rear surface 0 Rear surface 2.30354// L Front surface +0.22580/f L Front surface +0.86967/f l B Lenses Powers of Refraction Lenses Powers of Refraction Rear surface Rear Surface +0'8G967U An/R Ll surface Folsom/f Front Surface +058!!! It will be understood that each of the elements de- Rear surface 0 e sur 0 scribed above, or two or more together, may also find a Frontsmmce Frontsurme +m6144/f useful application in other types of ad ustable ob ectives L1 6 u------ R i 0 28756 differing from the types described above.

Surface "M583 U W Sm m If While the invention has been illustrated and described Front sur ace 7 /f L From Surface 0 as embodied in an adjustable projection objective having L3 Rear surface 0 1 Rear surface 2.34099/f a pair of simultaneously disolaceable lenses for varying 1 5 F t I +0 88496 the focal length of the ob ective, it 18 not intended to be L4 Fmntsmface +02 29 If M ace limited to the details shown, since various modifications Rear sur ace /f Rear Surface /f and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended Within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. An adjustable projection objective of variable focal length having an aperture of 1:1.1, comprising eight axially spaced lenses of which the second and third lenses are forwardly and rearwardly movable in the direction of the optical axis while maintaining a constant axial airspace, the objective as a whole having a total length of 2.78209) and being constructed substantially according to the specifications in the following table:

wherein the first column lists the eight lenses in numerals in the order from the front to the rear, wherein f is the focal length of the objective, m; is the index of refraction for the wave length 587.6 mg of the spectrum, and v is the dispersive index; and wherein R, d and I, refer,

are designated by successive numbers in the order from the front to the rear Lens Surfaces Powers of Lens Surfaces Powers of Refraction Refraction +8. 182941) +8. 43792/f 0 14586 +1.10l97/f 0 l4586/f 0. 30656/f 0 2l772/f 0 2. An adjustable projection objective of variable focal length having an aperture of 1:1.1, comprising eight axially spaced lenses of which the second and third lenses are forwardly and rearwardly movable in the direction of the optical axis while maintaining a constant axial airspace, the objective as a whole having a total length of 2.76866) and being constructed substantially according to the spec1ficat1ons 1n the following table.

Lenses Radii Thlcknesses no 12 Airspaces R =+3.15830f 1 di=0.12500f n1=1.56873 v =63.12

' l =variable Ra=-3.26340f 2 d,=0.07250f m=1.51680 v;=64.20

lz=0.12791f R =2.95840f 3 d3=0.07250f m=1.51680 v3=64.20

l =variable R1 =+2.67075f 4 d4=0.13673f m=1.56873 v4=63.12

l4=0.00800f R =+1.05955f 5 d =0.19000f n =l.62041 v =60.29

R =oo l =0.00500f R1 =+0.58450f 6 d =0.16480f m=1.62041 m=60.29

Ru=+2.15750f l =0.04621f R =oo 7 d1=0.21000f m=1.78470 v =26.10

Ri =+0.33520f Z =0.2859Of Ris=+0.853l0f s d3=0.13000f 115:1.75496 0 :53.28

Riu='0.853l0f wherein the first column lists the eight lenses in numerals in the order from the front to the rear, wherein f is the focal length of the objective, 11 is the index of refraction for the wave length 587.6 mg of the spectrum, and v is the dispersive index; and wherein R, d and I, refer,

respectively, to the radii of curvature of the refractive respectively, to the radii of curvature of the refractive surfaces, the axial thicknesses of the lenses, and the axial surfaces, the axial thicknesses of the lenses, and the axial airspaces between the lenses, the subscripts on the char- 1 airspaces between the lenses, the subscripts on the characters R, d and I being numbered consecutively from the acters R, d and I being numbered consecutively from the front to the rear, and the plus and minus signs in the front to the rear, and the plus and minus signs in the second column indicating refractive surfaces respectively second column indicating refractive surfaces respectively convex and concave to the front, the rear intercept length convex and concave to the front, the rear intercept length and focal length of the objective depending on the posiand focal length of the objective depending on the position of said second and third lenses as follows: tion of said second and third lenses as follows:

Variable Variable Rear Intercept Focal Length Variable Variable Rear Intercept Focal Length Airspace Airspace Length Airspace Airspace Length l1=0. 08749f li=1. 08023] 0. 29375; 0. 75172! li=0.07s00f Z;=1.1161lf 0.29737] 0.74884] 1i=0. 68768] Z==0. 48004f 0. 31374; 1. 00f Z1=0.69872f l =0.49539f 0.316111 1.00] 11 1. 12772, l==0. 040001 0. 32521] 7 1.252481 1i=1.15411j l3=0.04000f 032578) 1.24786] the actual powers of refraction, An/R of the surfaces of the lenses having substantially the values stated in the following tablein which the lens surfaces of all lenses the actual powers of refraction An/R of the surfaces of the lenses having substantially the values stated in the following table in which the lens surfaces of all lenses are designated by successive numbers in the order from the front to the rear Lens Surfaces Powers of Lens Surfaces Powers of Refraction Refraction +l18007/f +3.58554/f 0 --0.15836// +1.06l44/f 0.15836/f -0.28756/f O.l.7469/f 0 0 2.34099/f +0.2l295/f +0.88496/f +0.2l295/f +0.88496/f Lenses Radil Thicknesses no u Airspaces R1 =+3.17793f 1 d1=0.12500f n1=1.56873 vi=63.12

l =variab1e Ra=3.84882f 2 d,=0.01250f 1L1=L5168O vz=64.20

z=0.12791f R5 =2 31809f 3 .r d3=0.07250f n3=1.51680 v =64.2O

6f 1;: variable -R 2.5187 4 7 d4=0.13673f n4=1.56873 v4=63.l2

Ra 2.51876f 6 l4=0.00800f R 1.10 l a d =0.2l000f n =1.62041 v =60.29

f z,=0.00500f R 0.50300 f d =0 16480f m=1.62041 v =60.29 R 2.14080 l =0.04621f R =m 7 f d7=0.19700f n1=1.78470 :11=26.10

H Z1=0.Z8051f R 0.8 1 s di=0.13000f m=1.75496 v =53.28

Rm=0.86810f wherein the first column lists the eight lenses in numerals in the order from the front to the rear, wherein f is the focal length of the objective, n is the index of refraction for the wave length 587.6 m of the spectrum, and v is the dispersive index; and wherein R, d and I, refer, respectively, to the radii of curvature of the refractive surfaces, the axial thicknesses of the lenses, and the axial airspaces between the lenses, the subscripts on the character R, d and I being numbered consecutively from the front to the rear, and the plus and minus signs in the second column indicating refractive surfaces respectively convex and concave to the front, the rear intercept length and focal length of the objective depending on the position of said second and third lenses as follows:

Variable Airspace Variable Airspace Rear Intercept Focal Length Length Za=1.11451f Za=0.49481f la=0.04000f Powers of Lens Surfaces Refraction Powers of Refraction Lens Surfaces 0.13427/f 0.13427/f g.22294/f +1.10197/f g.28899/f References Cited UNITED STATES PATENTS 3,023,673 3/1962 Cox et a1. 8857 3,270,615 9/ 1966 Higuchi 8857 JEWELL H. PEDERSEN, Primary Examiner.

JOHN K. CORBIN, Examiner. 

1. AN ADJUSTABLE PROJECTION OBJECTIVE OF VARIABLE FOCAL LENGTH HAVING AN APERTURE OF 1:1.1, COMPRISING EIGHT AXIALLY SPACED LENSES OF WHICH THE SECOND AND THIRD LENSES ARE FORWARDLY AND REARWARDLY MOVABLE IN THE DIRECTION OF THE OPTICAL AXIS WHILE MAINTAINING A CONSTANT AXIAL AIRSPACE, THE OBJECTIVE AS A WHOLE HAVING A TOTAL LENGTH OF 2.78209F AND BEING CONSTRUCTED SUBSTANTIALLY ACCORDING TO THE SPECIFICATIONS IN THE FOLLOWING TABLE: 